This invention relates generally to particle separators of the type described in U.S. Pat. No. 4,199,443, and to combination particle detectors and foam separators of the type described in U.S. Pat. No. 4,282,016, the disclosures of which are incorporated herein by reference. Such devices are used in conjunction with hydraulic and lubrication systems for mechanical equipment which utilize a fluid such as oil. In particular, apparatus of the present invention selectively removes particles above a predetermined size in the oil of such systems. Preferred embodiments of the invention also remove air and other trapped gases from the fluid and vents them from the system.
Mechanical power transmission equipment is subject to wear due to abrasive friction, caused by the contact of moving parts under pressure or load at high relative speeds. This results in the release of a quantity of small particles. Such "wear particles" or "fuzz" are generally 2 to 20 microns in size. Particles of this size, when suspended in a circulating fluid such as heavy lubricating oil generally move with it rather than reacting promptly to gravity and inertial forces. However, once normal "wear in" occurs, the quantity of such particles reduces to a relatively low value, and in most systems, they are readily removed from the system by filters or, if the particles are ferrous, by magnets.
When the components of the power-transmitting system which is being lubricated become overloaded or when localized areas U.S. Pat. application of Aslin for Cyclonic System etc. of weakness occur, the situation changes radically. In such cases, much larger particles of material become loosened, generally at the point of contact between moving parts under high surface pressure. Furthermore, once the surface has been deformed by the breaking off of such particles, the rate of deterioration is accelerated, resulting in the breaking off of additional particles at increasing rates. These "failure particles" are generally of a much greater order of magnitude in size than the "wear particles" referred to previously. In addition, the quantities of wear particles produced are substantially increased. Failure particles generally fall into the 100 to 2000 micron size range. Due to their greater mass, they are less subject to being suspended in the lubricating fluid.
It is well known that the structural failure of drive train components may be predicted in advance of such failure by monitoring the condition of the lubricating oil. Such structural failure is indicated when metallic particles in the size range of failure particles, i.e. greater than 100 microns, are detected or when the quantity of wear particles substantially increases. The apparatus of the present invention is of the type which separates out such debris particles and provides a signal warning the operator of the occurrence of the situation.
In addition to generating particulate debris, power applications also tend to create a degree of churning of the lubricating fluid, resulting in the formation of foam which is often quite stable. In many systems, equal volumes of air and oil are mixed. In still other high speed applications, such as lubrication of gas turbines, as many as four parts of air may be mixed with one part of oil. Such dilution of the oil results in less oil coming into contact with the surfaces to be lubricated, thus diminishing the overall lubricating effect of the oil--an obviously undesirable result. U.S. Pat. application of Aslin for Cyclonic System etc. Moreover, when air is present in the oil, the fluid becomes compressible, thus lowering the overall pressure in the oil system. This is particularly true when positive displacement-type or centrifugal pumps are used, a common practice in these types of systems. In addition, the cooling effect of the oil is substantially reduced due to more friction because of air entrainment, which increases the probability of overheating and accelerated wear.